Mechanical-hydraulic transmission

ABSTRACT

A mechanical - hydraulic transmission for a crawler-type vehicle is provided having a reduced dimension in a widthwise direction perpendicular to input/output shafts and capable of ready installation on an existent crawler steering device. The transmission is arranged such that a power input shaft (1), directly connected to a prime mover, an intermediate shaft (9) and an output shaft (19), are concentrically related and arranged in a longitudinal column. Normal- and reverse-rotation planetary gear devices (5, 6), having respective clutches (7, 8) thereof, are mounted on a periphery of the power input shaft (1), and the power input shaft (1) is connected to a variable displacement hydraulic pump (2). A plurality of planetary gear trains (11, 12) having respective clutches (10, 13, 14) and a single planetary differential gear (15) are mounted on a periphery of the intermediate shaft (9), and an output side of the variable displacement hydraulic motor unit (20), driven by the hydraulic pump (2) and the output shaft (19), are connected to the planetary differential gear (15).

DESCRIPTION

1. Technical Field

This invention relates to a mechanical - hydraulic transmission which iscapable of selecting a plurality of driving speed modes in respectivedriving in forward- and rearward-movement directions.

2. Background Art

As a conventional transmission of the kind referred to above,transmissions are known which are disclosed in respective specificationsof U.S. Pat. No. 3,426,621 and Japanese Patent Laid-Open No. HEI 2 -14979.

Each of these publicly known forward- and rearward-movement multi-stagetransmitting mechanical - hydraulic transmissiones is so arranged as tobe provided with a mechanical power transmitting section of two- shaftparallel type.

The above-described former is so arranged that a transmitting sectionwhich modifies or alters a rotational direction and rotational speed ofinputted power is installed on a mechanical transmitting power inputsystem shaft which lays down so as to extend perpendicular to alongitudinal direction (fore and aft directions) of a vehicle body, apower output shaft system is juxtaposed in parallel with a mechanicalpower input system shaft, and mechanical - hydraulic transmitting poweris outputted in a power output shaft system direction.

Further, the latter of the aforesaid prior art is arranged such that apower transmitting system shaft lays down so as to extend perpendicularto a longitudinal direction of a vehicle body, a mechanical transmittingsection for changing or modifying a rotational direction and rotationalspeed of inputted power and a differential planetary gear mechanism ofcomposition of mechanical - hydraulic powers are installed in series inthe axial direction, and a static hydraulic transmitting device isjuxtaposed in parallel to the power transmitting system shaft, to outputthe mechanical - hydraulic transmitting power to both sides in awidthwise direction of the vehicle body.

In short, any one of these mechanical - hydraulic transmissions of theprior art is provided with crawler-belt steering devices of crawler-typevehicles on both outsides of the transmitting output system shafts, toexhibit transmitting and steering function.

In the above-mentioned prior art, in a manner in which mechanical -hydraulic transmitting power is outputted on both sides in the widthwisedirection of the vehicle body, and the crawler-belt steering devices areequipped on both sides of the output shaft, wide housing or storagespace is required in the widthwise direction of the vehicle body. Thismakes difficult loading of the transmission to an existent productionvehicle.

Such mechanical - hydraulic transmission has the following problems andthe like. That is, since the crawler-belt steering device is brought toexclusive one, it is impossible to combine the mechanical - hydraulictransmission with the existent crawler-belt steering device, there is noloading interchangeability with other existent transmitting devices withrespect to the same or identical rank vehicle, and the like.

Furthermore, the above-described prior art is an arrangement in which asingle clutch exclusive for each speed ratio is engaged, to thereby forma speed condition. For this reason, power transmitting paths extendingfrom the input shaft to a differential gear are required only for thenumber of speed ratios in parallel relation to each other. In a casewhere arrangements each having such clutch arrangement are disposed on asingle shaft so as to be capable of being loaded on an already existentproduction vehicle, since power transmission between the input shaft andthe differential gear is brought to a multiple hollow shaft, anarrangement thereof is complicated.

SUMMARY OF THE INVENTION

The invention has been done in view of the above, and an object of theinvention is to provide a mechanical - hydraulic transmission for acrawler-type vehicle, in which dimension in a widthwise direction isreduced; there is loading interchangeability with other speed-changetransmitting devices with respect to crawler-belt vehicles having thesame vehicle rank; and it is possible to freely select combination withan existent crawler-belt steering device.

In order to achieve the above-described objects, according to a main orchief mode of the invention, there can be provided a mechanical -hydraulic transmission comprising a mechanical power transmitting deviceand a static hydraulic power transmitting device arranged in parallelbetween a prime mover and an output shaft, in order to transmit power ofthe prime mover to the output shaft in a manner of infinitevariable-speed transmission, wherein the mechanical power transmittingdevice consists of a plurality of columns of planetary gear trains andconnected to a power input shaft directly connected to the prime mover,wherein the static hydraulic power transmitting device consists of avariable displacement hydraulic pump driven by the power from the powerinput shaft, and a hydraulic motor unit driven by the pump foroutputting the power to one of the planetary gear trains of themechanical power transmitting device, characterized in that themechanical power transmitting device is provided with three shaftsdisposed under three-piece fashion with respect to a concentricdirection, that is, a power input shaft, an intermediate shaft and anoutput shaft, that the power input shaft is provided with a normal-rotation and reverse-rotation input means in which normal- andreverse-rotational planetary gear devices are concentrically arrangedfor changing the input rotating direction of the power of the primemover to a normal rotating direction and a reverse rotating directionfor outputting the power selectively to the intermediate shaft; that theintermediate shaft is provided with a power transmitting system which isthe intermediate shaft per se, a planetary gear transmitting systemarranged concentrically on the intermediate shaft, and a planetarydifferential gear for connecting output sides of the respectivetransmitting systems to the output shaft through a plurality of columnsof planetary gear elements; that, on the other hand, the statichydraulic power transmitting device is provided with a gear train forconnecting the output shaft of the hydraulic motor unit to the planetarygear element of the planetary differential gear; that the planetary geartransmitting system provided in the intermediate shaft is provided withclutch means for driving the output shaft only by the planetarydifferential gear which is operated by the static hydraulic powertransmitting device in one driving mode, and both clutch means forselecting modification or change of the rotational direction which isdone by the normal and reverse input means and clutch means forselecting modification or change of speed ratio which is done by thepower transmitting system which is the intermediate shaft per se, theplanetary gear transmitting system and the planetary transmitting geardue to the intermediate shaft are provided in other driving modes; andthat combination thereof has a plurality and same number of speed gearratios both in normal- and reverse-rotation.

In the above-mentioned mechanical - hydraulic transmission of theapparatus according to the invention, the power from the prime mover istransmitted both by the static hydraulic power transmitting device andthe mechanical power transmitting device. Power from both powertransmitting devices are transmitted to the output shaft through theplanetary differential gear of the mechanical power transmitting device.

A first speed ratio of forward and reverse movements is performed onlyby operation of the static hydraulic power transmitting device under acondition that a first-speed ratio clutch of the mechanical powertransmitting device is engaged. Moreover, second and third speed ratiosfor forward and reverse movements are performed by the fact thatforward-movement or rearward-movement clutch of the mechanical powertransmitting device is selectively engaged, clutches for second andthird speed ratios are selectively engaged, and in parallel therewith,the power from the static hydraulic power transmitting device isinputted to the planetary differential gear of the mechanical powertransmitting device.

At this time, both powers are composited by the planetary differentialgear and are transmitted to the output shaft.

According to the mechanical - hydraulic transmission of the invention,the arrangement is such that the power input shaft thereof, theintermediate shaft and the output shaft are arranged in series on thesame axis. Thus, the following advantages can be produced. That is, itis possible to narrow or reduce the lateral dimension of thetransmission portion similarly to the conventional mechanicaltransmission. The mechanical - hydraulic transmission can be loaded ontoa crawler-type vehicle such as a bulldozer or the like without great orlarge design modification or alteration. Furthermore, there is loadinginterchangeability with other transmission transmitting devices withrespect to the crawler-type vehicle of the same vehicle level, and it ispossible to freely select combination with existent crawler steeringdevice.

The aforesaid and other objects, modes and advantages of the presentinvention will become apparent to one skilled in the art, by thedescription with reference to the following description and the attacheddrawings in which a preferred specific embodiment coincident with theprinciple of the present invention is indicated as an embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an entire schematic arrangement view showing a specificembodiment of the invention;

FIG. 2 is a diagram showing the relationship of the number ofrevolutions of a variable displacement hydraulic motor unit with respectto the number of revolutions of an output shaft; and

FIG. 3 is a schematic arrangement view for explanation, showing atransmission and a steering device in separation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the invention will hereunder be described in detailwith reference to the accompanying drawings.

In the figure, the reference numeral 1 denotes a power input shaft of amechanical - hydraulic transmission which is connected in seriesconcentrically to an output shaft of a prime mover (not shown); and 2and 3, first and second variable displacement hydraulic pumps,respectively, which are connected to the power input shaft 1 throughgear trains. The pump 3 is utilized as a pump for hydraulic steering.The reference numeral 4 denotes a charge pump which is connected to thepower input shaft 1 through a gear train.

The power input shaft 1 is provided with two planetary gear trains, thatis rearward-movement (reverse-rotation) and forward-movement(normal-rotation) planetary gear trains 5 and 6 in an axial direction ofthe power input shaft 1.

The rearward-movement planetary gear train 5 comprises a sun gear 5aconnected to the power input shaft 1, a carrier 5d provided with arearward-movement clutch 7 for being selectively arrested or restrictedin free rotation, a planetary gear 5b supported by the carrier 5d and inmesh with the sun gear 5a and an annular internal gear 5c in mesh withthe planetary gear 5b, to inhibit or suppress revolution of theplanetary gear 5b and to transform a rotational direction from the sungear 5a to a reversed direction to transmit the rotational directionfrom the annular gear 5c.

The forward-movement planetary gear train 6 comprises a sun gear 6aconnected to the power input shaft 1, a carrier 6d integral with theannular gear 5c of the rearward-movement planetary gear train 5, aplanetary gear 6b supported by the carrier 6d and in mesh with the sungear 6a, and an annular internal gear 6c in mesh with the planetary gear6b and provided with a forward-movement clutch 8 for selectivelyarresting free rotation, to arrest free rotation of the annular gear 6cand to rotate the carrier 6d in the same rotational direction as the sungear 6a by rotation and revolution of the planetary gear 6b to therebytransmit the rotation.

The annular gears 5c and 6c of both the respective planetary gear trains5 and 6 and a first connecting element 100 of the carrier 6d areincluded in a speed ratio change device. A clutch 10 for second gearspeed, and first and second planetary gear trains 11 and 12 for thirdgear speed are arranged in series with respect to an axial direction.

The clutch 10 for second gear speed selectively connects the firstconnecting element 100 and an intermediate shaft 9 arrangedconcentrically and in series with respect to the power input shaft 1 toeach other, to receive the power to the intermediate shaft 9.

The first planetary gear train 11 for third gear speed is in mesh with aplanetary gear 11b in which the first connecting element 100 is broughtto an annular internal gear 11c, and which is supported by a carrier 11dwhich is provided with a clutch 13 for third gear speed for selectivelyarresting or suppressing rotation of the annular internal gear 11c. Theplanetary gear 11b and sun gear 11a are in mesh with each other.Revolution of the planetary gear 11b is stopped. The sun gear 11a isdriven at a speed-increasing ratio of the annular internal gear versusthe sun gear. The power from the power input shaft 1 is received.

The received power is further speed-increased by the second planetarygear train 12 for third gear speed.

The second planetary gear train 12 for third gear speed consists of anannular internal gear 12c integrally connected to the sun gear 11a ofthe first planetary gear train 11 for third speed ratio through a secondconnecting element. 101, a fixed carrier 12d, a planetary gear 12bsupported by the fixed carrier 12d and in mesh with the annular internalgear 12c, and a sun gear 12a in mesh with the planetary gear 12b. Powertransmitted from the first planetary gear train 12 for third speed ratiothrough the second connecting element 101 rotates the planetary gear12b, and is speed-increased by a speed-increasing ratio due to theannular internal gear versus the sun gear, to drive the sun gear 12a.

The power selectively received from the above-mentioned intermediateshaft 9 and sun gear 12a continues to the power output portion.

The power output portion is brought to a planetary differential gear 15.The planetary differential gear 15 consists of first and seconddifferential planetary gear trains 16 and 17 which are arrangedconcentrically with respect to the intermediate shaft 9 on the outputside of the intermediate shaft 9.

The first differential planetary gear train 16 of the planetarydifferential gear 15 is a double planetary gear type and includes a gearelement in which double planetary gears 16b and 16b' in mesh with eachother is arranged on a carrier 16d, one of the planetary gears 16b is inmesh with the sun gear 16a, and the other planetary gear 16b' is in meshwith an annular internal gear 16c.

Moreover, the second differential planetary gear train 17 is singleplanetary gear type and includes a sun gear 17a in mesh with a planetarygear 17b mounted on a carrier 17d, and a gear element of an annularinternal gear 17c in mesh with the planetary gear 17b.

The sun gear 16a of the first differential planetary gear train 16 isintegrated with the sun gear 12a of the second planetary gear train 12for third gear speed by a tubular third connecting element 102, and isconnected to a transmitting system of mechanical power. The thirdconnecting element 102 has a clutch hub 103 which spreads in a radialdirection substantially at an intermediate portion on the outerperipheral side thereof. The clutch hub 103 is engaged with a clutch 14for first speed ratio.

The carrier 16d of the first differential planetary gear train 16 isjoined or coupled to the sun gear 17a of the second differentialplanetary gear train 17 through the fourth connecting element 104, andis further connected to a variable displacement hydraulic motor unit 20of the static hydraulic power transmitting device through a fifthconnecting element 105 and a gear train 21 including a gear 18integrated with the fifth connecting element 105. The first and seconddifferential planetary gear trains 16 and 17 introduce the power due tothe static hydraulic power transmitting device into an input system.

The second differential planetary gear train 17 connects a carrier 17dto the intermediate shaft 9, and is coupled to a transmitting system ofmechanical power of a different system. Furthermore, the annularinternal gear 17c is coupled to an output shaft 19.

Further, the first and second differential planetary gear trains 16 and17 connect the annular internal gear 16c of the first differentialplanetary gear train 16 and the carrier 17d of the second differentialplanetary gear train 17 to each other through a sixth connecting element106 by connection or joint.

The output shaft 19 is located in a direction concentric with theintermediate shaft 9 and in series therewith, and has a bevel gear 23aat a shaft end.

The variable displacement hydraulic motor unit 20 is connected to thevariable displacement hydraulic pump 2 by piping.

The reference numeral 22 denotes a steering device. The steering device22 has an input shaft 23 which is disposed in triangle with respect tothe output shaft 19 of the planetary differential gear 15, and isconnected to the output shaft 19 by the bevel gear mechanism 23a. A pairof left- and right-hand steering differential planetary gear trains 24aand 24b are arranged respectively on both sides of the input shaft 23 inthe axial direction. The input shaft 23 has ends thereof which areconnected respectively to first input elements 25a and 25b of therespective gear trains 24a and 24b. One 26a of second input elements 26aand 26b of the respective gear trains 24a and 24b is connected to anoutput shaft of a steering hydraulic motor 28 through thenormal-rotation gear train 27a.

The other second input element 26b is connected to the output shaft ofthe steering hydraulic motor 28 through a reverse-rotation gear train27b. Output shafts 29a and 29b of the respective steering differentialplanetary gear trains 24a and 24b are connected respectively to left-and right-hand drive driving wheel shafts (not shown). The referencenumerals 30a and 30b denote left- and right-hand brakes, respectively.The second hydraulic motor 28 is connected to the second variabledisplacement hydraulic pump 3 through piping, and is driven by deliveryhydraulic pressure of the pump 3.

In the above-described constitutional elements, the rearward-movementand forward-movement planetary gear trains 5 and 6 from the power inputshaft 1, the other planetary gear trains 11, and 12, the clutches 13 and14, and the planetary differential gear 15 are accommodated within acase 32 as parts of a mechanical power transmitting device 31 as shownin FIGS. 1 and 3.

Further, the steering device 22 is similarly accommodated within asingle case 33 as shown in FIG. 3.

A rearward end portion of the case 32 of the mechanical powertransmitting device 31 and a front end portion of the case 33 of thesteering device 22 are provided respectively with flange portions 32aand 33a which are engageable with and disengageable from each other.Both the flanges 32a and 33a are joined to each other by bolts 34engagingly and disengagingly.

Operation of the mechanical - hydraulic transmission arranged asdescribed above will be described.

The mechanical - hydraulic transmission has three speed driving modes ineach of the forward-movement and rearward-movement directions, andperforms power transmission operation continuously variable in speed.

A first speed ratio driving mode is achieved by output speeds in theforward-movement direction and in the rearward-movement direction dueonly to the static hydraulic power transmitting device under a conditionthat the clutch 14 for first speed ratio is engaged, and the clutches 10and 13 for second speed ratio and third gear speed capable of selectiveoperation are released or under a condition that the first gear speedand second speed ratio clutches 14 and 10 are engaged, and the thirdspeed ratio clutch 13 is released.

A second speed ratio driving mode is achieved by a mechanical -hydraulic second speed ratio mode in which the clutch 14 for first speedratio and the clutch 13 for third speed ratio are released, and eitherone of the forward- and rearward-movement clutches 7 and 8 for selectingthe rotational direction of the input power due to the mechanical powertransmitting device and the two clutches of the clutch 10 for secondspeed ratio are engaged with each other.

A third speed ratio driving mode is achieved by a mechanical - hydraulicthird speed ratio mode in which the clutch 14 for first speed ratio andthe clutch 10 for second speed ratio are released, and either one of theforward- and rearward-movement clutches 7 and 8 for selecting therotational direction of the input power due to the mechanical powertransmitting device and two clutches of the clutch 13 for third gearspeed ratio are engaged with each other.

Operation of the static hydraulic power transmitting device in theabove-described operation will next be described.

(1) The variable displacement hydraulic pump 2 of the static hydraulicpower transmitting device is of alternating variable displacement type.The variable displacement hydraulic motor unit 20 is of one-sidevariable displacement type, and an exit and an entrance thereofcommunicate with each other (in the following description, the variabledisplacement hydraulic pump and the variable displacement hydraulicmotor unit will be referred simply to "pump" and "motor unit",respectively).

When swash-plate angle of the pump 2 is inclined in a positive directionfrom 0° under the condition that the swash-plate angle of the motor unit20 is the maximum (maximum in displacement), the number of revolution ofthe motor unit 20 increases from 0 in the positive direction. If theswash-plate angle of the motor unit 20 is reduced under the conditionthat the swash-plate angle of the pump 2 is the maximum, the number ofrevolution of the motor unit 20 further increases.

Reversely, when the swash-plate angle of the pump 2 is inclined in thenegative direction from 0°, the number of revolution of the motor unit20 is reduced from 0 in the negative direction.

In this manner, it is possible to vary a motor speed ratio (a value inwhich the number of revolution of the motor is divided by the number ofrevolution of the power input shaft 1) in a infinite variable-speedmanner from normal rotation to reverse rotation.

Alternatively, the second speed ratio clutch 10 may be engaged inaddition to the first speed ratio clutch 14 upon the above-describedfirst gear speed operation.

By doing so, a speed ratio of the output shaft upon the first speedratio is brought to specific values e_(F1) (at forward movement) ande_(R1) (at rearward movement). When the relative number of rotation ofthe forward-movement clutch 8 or the rearward-movement clutch 7 isbrought to 0, the respective clutches are engaged, and the first gearspeed clutch 14 is released, whereby a condition is smoothly brought tothe two gear speed condition including the forward movement and therearward movement.

(2) In forward- and rearward-movement first speed ratio (F1, R1), thetransmission is performed only by the static hydraulic powertransmitting device.

That is, only the clutch 14 for first speed ratio (1st) is engaged. Bydoing so, the sun gear 16a of the first differential planetary geartrain 16 of the planetary differential gear 15 is fixed or stationary.

Under this condition, the power from the motor unit 20 is inputted tothe input gear 18 of the planetary differential gear 15 from the geartrain 21, and is transmitted to the output shaft 19 successively throughthe carrier 16d, the double planetary gears 16b and 16b' and the linkgear 16c of the first differential planetary gear train 16, and thecarrier 17d, the planetary gear 17b and the ring gear 17c connected tothe output shaft 19, of the second differential planetary gear train 17.

When the velocity or speed ratio of the motor unit 20 increases in apositive direction from 0 under this condition, the speed ratio istransmitted to the output shaft 19 through the two columns ofdifferential planetary gear trains 16 and 17 of the planetarydifferential gear 15. The number of revolution of the output shaft 19increases from 0 in the positive direction. Conversely, when the motorspeed ratio decreases from 0 in the negative direction, the number ofrevolution of the output shaft 19 decreases from 0 in the negativedirection.

In this manner, it is possible to vary the speed ratio of the outputshaft of the static hydraulic power transmitting device (a value inwhich the number of revolution of the output shaft 19 is divided by thenumber of revolution of the power input shaft 1) within positive andnegative ranges in an infinite variable-speed manner.

FIG. 2 indicates the number of revolution Nv of the output shaft 19 withrespect to variation in the number of revolution of the motor unit 20.In the differential of first gear speed, the number of revolution N ofthe motor unit 20 is controlled along a-b, whereby the number ofrevolution Nv of the output shaft 19 can be controlled to the forward-and rearward-movement first speed ratio from 0.

In connection with the above, in a case of forward movement at operationof the first gear speed, the forward-movement clutch 8 may be engaged.While, in a case of the rearward movement, the rearward-movement clutch7 may be engaged. By doing so, the speed ratio of the output shaft atthe first speed ratio is brought to specific values e_(F1) (at forwardmovement) and e_(R1) (at rearward movement). When the relative number ofrevolution of the clutch 10 for second speed ratio of the forwardmovement or the rearward movement is brought to 0, the clutch 10 forsecond speed ratio is engaged, and the clutch 14 for first speed ratiois released, whereby the vehicle is smoothly brought to a two-speedcondition including the forward movement or the rearward movement.

(3) On the side of low speed of forward-movement second speed ratio(F2):

The first speed ratio (1st) clutch 14 is released beyond the first speedrange under the forward-movement first speed ratio control, and theforward-movement (F) clutch 8 and the second speed ratio (2nd) clutch 10are engaged with each other, whereby a condition is brought to theforward-movement second speed ratio condition.

By doing so, the power of the power input shaft 1 is reduced in speedand is transmitted from the forward-movement planetary gear train 6 tothe intermediate shaft 9 through the second speed ratio clutch 10. Bythe intermediate shaft 9, the reduced speed is outputted to the outputshaft 19 integral with the annular internal gear 17c, from the carrier17d of the second differential planetary gear train 17 of the planetarydifferential gear 15 through the planetary gear 17b.

Further, at this time, a reaction force occurring in the planetarydifferential gear 15 is transmitted from the planetary gear 17b of thesecond differential planetary gear train 17 to the input gear 18 of thedifferential gear 15 through the sun gear 17a and the carrier 16b of thesecond differential planetary gear train 16. By doing so, the outputshaft of the motor unit 20 is driven in a reverse direction. The powerdue to the reaction force of the planetary differential gear 15 isreturned to the input shaft 1 through the variable displacementhydraulic pump 2.

That is, under the condition that the motor speed ratio is positive atthe forwards-movement second speed ratio, the motor unit 20 performs apumping action to drive the pump 2, and is composited with the powerfrom the power input shaft 1, to transmit the power to the planetarydifferential gear 15. A part of the power from the differential gear 15drives the motor unit 20, and the remaining power drives the outputshaft 19.

Revolution of the motor unit 20 at this time changes or varies along b-cin FIG. 2. The point c is a position where the swash plate of the motorunit 20 is brought to neutral, and the number of revolution thereof isbrought to zero.

(4) On the side of high speed of the forward-movement second speed ratio(F2):

When the number of revolution of the motor unit 20 varies along c-d inFIG. 2 so that the speed ratio decreases, the output shaft 19 increasesin speed so as to be brought to the side of the high speed of secondspeed ratio.

That is, when the motor speed ratio is under the negative condition, apart of the power from the power input shaft 1 drives the pump 2, and istransmitted to the planetary differential gear 15 through the motor unit20. The remaining power is transmitted to the planetary differentialgear 15 through the gear train. At the planetary differential gear 15,both the powers are composited to drive the output shaft 19.

(5) On the side of low speed of forward-movement third speed ratio (F3):

In the forward-movement second gear speed control, when the speed ratioof the motor unit 20 is decreased so that the speed ratio of the outputshaft is brought to the specific value e_(F2), the relative number ofrevolution of the third speed ratio clutch 13 is brought to 0. At thistime, the third gear speed clutch 13 is engaged, and the second speedratio clutch 10 is released, whereby a condition is brought to a thirdspeed ratio condition.

By doing so, the power of the power input shaft 1 is inputted to the sungear 16a of the first differential gear train 16 of the planetarydifferential gear 15 from the forward-movement planetary gear train 6through the third gear speed first planetary gear train 11 and thesecond planetary gear train 12. In the planetary differential gear 15,the power is composited by the first and second differential gear trains16 and 17 and is transmitted to the output shaft 19. Under thiscondition, when the motor speed ratio increases, the number ofrevolution of the output shaft 19 increases.

The number of revolution of the motor unit 20 at this time varies alongd-e in FIG. 2.

In this manner, under a condition that the motor speed ratio is negativeat the forward-movement third gear speed, the motor unit 20 performs thepumping action to drive the pump 2. The power is composited with thepower from the power input shaft 1 and is transmitted to the firstplanetary gear train 16 of the planetary differential gear 15. A part ofthe power from the first planetary gear train 16 drives the motor unit20, and the remaining power drives the output shaft 19 through thesecond planetary gear train 17.

(6) On the side of high speed of forward-movement third speed ratio(F3):

When the rotational direction of the motor unit 20 changes to the normalrotation and varies along e-f in FIG. 2, that is, under the conditionthat the motor speed ratio is positive at the forward-movement thirdspeed ratio, a part of the power from the power input shaft 1 drives thepump 2, and is transmitted to the first planetary gear train 16 of theplanetary differential gear 15 through the motor unit 20. The remainingpower is transmitted similarly to the first planetary gear train 16 ofthe differential gear 15 through each of the planetary gear trains. Thepowers are composited at the first planetary gear train 16 to drive theoutput shaft 19 through the second planetary gear train 17.

When the motor speed ratio decreases at the forward-movement third speedratio so that the speed ratio of the output shaft is brought to thespecific value e_(F2) (the same as the speed ratio at which switching ismade from the forward-movement second speed ratio to theforward-movement third speed ratio), the relative number of revolutionof the second speed ratio clutch 10 is brought to 0. At this time, whenthe second speed ratio clutch 10 is engaged and the third speed ratioclutch 13 is released, a condition is brought to a forward-movementsecond speed ratio.

The above-described operations (2), (3), (4) and (5) show the low speedside and the high speed side of the respective second speed ratio˜thirdspeed ratio on the side of the forward movement. However, the low speedside and the high speed side of the respective second speed ratio˜thirdspeed ratio on the side of the rearward movement is controlled similarlyto the side of forward movement by the fact that the rearward-movement(R) clutch 7 is engaged in place of the forward-movement (F) clutch 6with respect to the side of forward movement.

At this time, revolution of the motor unit 20 is such that, in FIG. 2,the low-speed side of rearward-movement second speed ratio (R2) changesalong a-g, the side of high speed thereof changes along g-h, the lowspeed side of rearward-movement third speed ratio (R3) changes alongh-i, and the high speed side thereof changes along i-j.

An example of the rearward-movement second speed ratio will hereunder bedescribed as an example of the rearward-movement operation.

At the rearward-movement second speed ratio, the power from the powerinput shaft 1 decreases in speed through the rearward-movement planetarygear train 5 and the second speed ratio clutch 10 and is transmitted tothe second planetary gear train 17 of the planetary differential gear15. On the other hand, the power from the motor unit 20 also decreasesand is transmitted to the second planetary gear train 17. At the secondplanetary gear train 17, the two powers are composited and aretransmitted to the output shaft 19. Under this condition, when the motorspeed ratio increases, the speed ratio of the output shaft 19 decreasesin the negative direction.

Under the condition that the motor speed ratio is negative at therearward-movement second speed ratio, the motor unit 20 performs thepumping action to drive the pump 2, and is composited with the powerfrom the power input shaft 1 so that the power is transmitted to thesecond planetary gear train 17 of the planetary differential gear 15through the rearward-movement planetary gear train 5 and the secondspeed ratio clutch 10. A part of the power from the second planetarygear train 17 drives the motor unit 20, and the remaining power drivesthe output shaft 19.

Furthermore, under the condition that the motor speed ratio is positive,a part of the power from the power input shaft 1 drives the pump 2 andis transmitted to the second planetary gear train 17 of the planetarydifferential gear 15 through the motor unit 20. The remaining power istransmitted to the second planetary gear train 17 through therearward-movement planetary gear train 5 and the second speed ratioclutch 10. The powers are composited by the second planetary gear train17 to drive the output shaft 19.

Under the condition of the rearward-movement second speed ratio, whenthe motor speed ratio increases so that the speed ratio of the outputshaft is brought to the specific value e_(R2), the relative number ofrevolution of the third speed ratio clutch 13 is brought to 0. At thistime, if the third speed ratio clutch 13 is engaged and the second speedratio clutch. 10 is released, a condition is brought to therearward-movement third speed ratio.

Further, when the motor speed ratio decreases at the rearward-movementsecond speed ratio so that the speed ratio of the output shaft isbrought to the specific value e_(R1) (the same as the speed ratio atwhich switching is made from the rearward-movement first speed ratio tothe rearward-movement second speed ratio), the relative number ofrevolution of the first speed ratio clutch 14 is brought to 0. At thistime, when the first speed ratio clutch 14 is engaged and the secondspeed ratio clutch 10 is released, a condition is brought to arearward-movement first speed ratio condition.

The power from the prime mover is transmitted to the output shaft 19 ofthe differential gear 15 in a manner described above. However, theoutput from the output shaft 19 is transmitted to the input shaft 23 ofthe steering device 22 through the bevel gear mechanism 23a, and isoutputted to the left- and right-hand output shafts 29a and 29b throughthe left- and right-hand steering differential planetary gear trains 24aand 24b.

At this time, the left- and right-hand steering differential planetarygear trains 24a and 24b are controlled by the steering hydraulic motor28, whereby a rotational difference occurs between the left- andright-hand output shafts 29a and 29b so that steering operation isperformed.

Since the steering device 22 is such that the case 33 accommodating thesame is mounted detachably with respect to the case 32 of the mechanicalpower transmitting device 31, it is possible to easily separate the case33 from the case 32 of the mechanical power transmitting device 31. Bydoing so, the mechanical power transmitting device 31 and the steeringdevice 22 can respectively be replaced with another one. In thisconnection, in this case, the bevel gear mechanism 23a which connectsthe output shaft 19 and the input shaft 23 to each other requires usingthe same one.

We claim:
 1. A mechanical - hydraulic transmission including a mechanical power transmitting device and a static hydraulic power transmitting device arranged in parallel between a prime mover and an output shaft, in order to transmit power from said prime mover to said output shaft in an infinitely variable-speed transmitting manner, wherein said mechanical power transmitting device has a plurality of columns of planetary gear trains connected to a power input shaft directly connected to the prime mover, and said static hydraulic power transmitting device has a variable displacement type hydraulic pump driven by power from said power input shaft and a hydraulic motor unit driven by said pump to output power thereof to one of the planetary gear trains of said mechanical power transmitting device, characterized in that said mechanical power transmitting device is provided with three shafts concentrically arranged in three-piece fashion with respect to a concentric direction, including said power input shaft, an intermediate shaft and said output shaft; that said power input shaft is provided with a forward-rotation and a reverse-rotation input means in which forward-rotation and reverse-rotation planetary gear devices are concentrically arranged and effective to change the input rotating direction of the power of the prime mover to a forward rotating direction and a reverse rotating direction for selectively outputting power to the intermediate shaft; that said intermediate shaft is provided with a power transmitting system including said intermediate shaft, a planetary gear transmitting system containing said planetary gear trains arranged on said intermediate shaft concentrically thereto, and a planetary differential gear for connecting output sides of the respective planetary gear trains contained in the planetary gear transmitting system to said output shaft through a plurality of columns of planetary gear elements arranged concentrically with respect to said intermediate shaft; that said static hydraulic power transmitting device is provided with a gear train connecting an output shaft of the hydraulic motor unit to a planetary gear element of said planetary differential gear; and that the planetary gear transmitting system on said intermediate shaft is provided with clutch means for driving the output shaft only by the planetary differential gear operated by the static hydraulic power transmitting device in one driving mode, and clutch means for selecting both change of a rotational direction performed by said forward and reverse input means and a change in speed which is performed by the power transmitting system including the intermediate shaft, the planetary gear transmitting system and the planetary differential gear, whereby a forward- and reverse-rotation input means is provided and the entire mechanical power transmitting device is arranged on a single axis.
 2. A mechanical - hydraulic transmission according to claim 1, characterized in that an input side of the power transmitting system including said intermediate shaft is connected to an output side of the forward- and reverse-rotation input means of said power input shaft through an associated clutch means; that the planetary gear transmitting system provided concentrically on the intermediate shaft includes said plurality of planetary gear trains; and that one of the planetary gear trains is connected through another clutch means capable of connecting/intercepting the output from said forward- and reverse-rotation input means to provide both forward- and rearward-movement having a plurality of speed ratios by combination of forward- and reverse-rotation switching clutches and speed-gear-ratio switching clutches.
 3. A mechanical - hydraulic transmission according to claim 1, characterized in that said planetary differential gear includes a first differential planetary gear train of double planetary gear type and a second differential planetary gear train of single planetary gear type; that a carrier of said first differential planetary gear train is connected to a sun gear of the second differential planetary gear train and the output shaft of said hydraulic motor unit; that an annular gear of the first differential planetary gear train is connected to a carrier of the second differential planetary gear train; that a sun gear of the first differential planetary gear train is connected to an output side of said planetary gear transmitting system which is arranged concentrically on the intermediate shaft; that a carrier of the second differential planetary gear train is connected to an output side of the intermediate shaft; and that an annular gear of the second differential planetary gear train is connected to said output shaft. 